Electric heaters



Dec. 13, 1955 A. c. 80665 2,727,120

ELECTRIC HEATERS Filed March 8, 1952 2 Sheets-Sheet l n I3 32. 3| 22. l5[6 la Z5 M 2.8

(IIIIIIIIIIII/ \NVENTOP. 9;:1EN 50 ATTORN EY Dec. 13, 1955 c; BQGGS2,727,120

ELECTRIC HEATERS Filed March 8, 1952 2 Sheets-Sheet 2 25 ALBEN C. (50665INVENTOR ATTORNEY United States Patent ELECTRIC HEATERS Albeu C. Boggs,Pittsburgh, Pa., assignor to Edwin L.

Wiegand Company, Pittsburgh, Pa., a corporation of Pennsylvania Thisinvention pertains to electric heaters, and to a method of making suchheaters, and the principal object of the invention is to provide new andimproved electric heaters, particularly in respect to the terminalportions thereof.

The invention is particularly adapted for use with a sheathedembedded-resistor electric heater wherein the resistor element isdisposed within the sheath and is embedded in an electrical insulatingheat conducting refractory material, and for illustrative purposes onlythe invention will hereinafter be described in connection with anelectric heater comprising a tubular metallic sheath having a resistorelement therein embedded in an electric insulating heat conductingrefractory material, and in which the terminal of the resistance elementextends outwardly from an open end of the tubular sheath.

That the refractory embedding material must be thoroughly dry andprotected against moisture in order to preserve the insulatingcharacteristics of the refractory material is well known, and that theprovision of a protective closure or seal has presented a considerableproblem is evidenced by various prior art patents illustrating, forexample, the use of materials such as glass, Bakelite, and solid rubberplugs as a closure medium.

In the embodiment herein illustrated, the refractory material isterminated short of the opening in the sheath to provide a pocket orchamber, and such opening is sealed in some satisfactory manner. Asherein illustrated, the seal provided to close the opening in the sheathand protect the refractory material from the deteriorating effect ofmoisture is preferably initially flowable partially cured or uncuredrubber-like adherent material which is or becomes and remains elastic. Acover or bushing having an opening therein through which the terminalpin connected to the resistor element passes, covers the opening in thesheath in a manner to closely confine the sealing material within thepocket or chamber, means being provided for maintaining the cover orbushing in closely overlying relation with the opening in the sheath tothereby confine the rubber-like material within a predetermined area.

A moldable vulcanizable rubber-or rubber-like material is then appliedto the exterior of the sheath adjacent the opening therein in suchmanner as to surround the sheath and to completely cover the closure orbushing applied to the opening in the sheath, as well as the protrudingend of the terminal pin, an electrical conducting wire attached to theterminal pin, and at least a portion of the length of the usualinsulation which covers an electrical conducting wire. This rubber orrubber-like material is then shaped by the use of a mold and theapplication of heat to form the material into a continuous cover whichis adhered to the exterior of the sheath adjacent the opening thereinand to at least the leading end of the insulation for the electricalconducting wire, thereby closing the entire assembly against access tovapors or moisture to the refractory embedding material.

In order to facilitate tight sealing engagement of th electricinsulating material. illustrated, the cover or bushing is provided withan axial 2,121,120 Patented Dec. 13, 1955 moldable vulcanizable rubberwith the exterior of the sheath adjacent the opening therein there isprovided a sleeve or ferrule of a material, for example, brass, which iscompatible with the moldable vulcanizable rubber insofar as the moldablevulcanizable rubber tightly adhering thereto when molded thereabout andsubjected to heat. Such sleeve or ferrule surrounds the outercircumference of the sheath adjacent the opening therein and is securedto the exterior of the sheath in a manner to prevent leakage of moisturebetween the inner circumference of the sleeve and the outercircumference of the sheath. Such sleeve or ferrule is also providedwith an annular flange or shoulder adjacent the end thereof away fromthe opening in the sheath, the flange or shoulder cooperating with themold for shaping the moldable vulcanizable rubber in a manner to preventextrusion of the moldable vulcanizable rubber outwardly of the mold andalong the length of the sheath, and also acting as a stop to preventextrusion of the heater sheath out of the cavity by pressure developedin the cavity during the molding cycle.

Various other objects and advantageous features of the invention may behad from the following description when taken in conjunction with theaccompanying drawings wherein:

Figure 1 is a fragmentary view, partly in elevation and partly insection, showing a terminal construction for a sheathed heater embodyingthe ideas of this invention;

Figure 2 is a view similar to Figure 1, but showing the covering ofmoldable vulcanizable material applied to the terminal end of theheater;

Figure 3 is an elevation of the fragmentary portion of the heater shownin Figure 2;

Figure 4 is a perspective view illustrating a form of mold for applyingthe moldable vulcanizable cover to the terminal portion of the heater;

Figure 5 is a view, partly in elevation and partly in section, showing amodified form of sleeve or ferrule;

Figure 6 is a view similar to Figure 5, but showing the idea of thisinvention applied to the opposite ends of a hairpin bent heater; and

Figure 7 is a view similar to Figure 6, but showing sleeves or ferrulesas shown singly in Figures 1, 2, and 3.

The heater shown in Figures 1, 2, and 3 is of the type commonly used forheating liquids and comprises a resistor 11 designed for the passage ofan electric current and consequent generation of the desired heat, aterminal pin 12 to which the end of the resistor element 11 is suitablysecured, a sheath 13 suitable to the temperatures to be experienced, andcommonly of metal, and refractory material 14 embedding the resistor 11and the inner end of the terminal pin 12 and serving both toelectrically insulate the resistor element and the terminal pin and alsoto conduct heat from the resistor element to the sheath.

The heater element illustrated may be bent upon itself providing a bodyportion suitable to be inserted into the liquid to be heated, with theterminal portions thereof extending through an opening in the wall of atank or other vessel. It will be understood, however, that the heaterelement may be of a single length, with one end being formed by a closedsheath and the opposite end including the terminal construction hereinillustrated, and that the heater element may be utilized for otherpurposes than the heating of liquids.

In the illustrated embodiment, the refractory material 14 is notextended to the open end of the sheath 13, or is routed out short of theend of the sheath, to thereby provide a pocket or chamber 15 adjacentthe open end of the sheath. The open end of the sheath is provided witha closure or bushing 16, preferably of ceramic or similar In theembodiment here.

bore 17 and a shank 18 which extends into the pocket at the open end ofthe sheath, the shank 18 being externally smaller than the interior ofthe pocket and internally larger than the exterior of the terminal pin12. If desired, the axial bore 17 may comprise successively differentdiameters, and the lowermost end of the shank may be tapered in adirection away from the terminal pin 12.

Another element of the closure comprises an elastic material 22 fillingthe spaces between the. lower end of the shank 18 and the upper surfaceof the refractory material 14, between the exterior of the terminal pin12 and the interior of the shank 123, and between the outer diameter ofthe shank 18 and the interior walls of the pocket 15. This material isformed in position, for example, by placing a proper quantity of thematerial in the pocket 15 within the sheath terminal portion and thenapplying the cover or bushing 16, forcing the shank 18 of the cover orbushing into the material, and thus forcing the material to flowupwardly into the spaces between the exterior of the terminal pin 12 andthe interior of the shank 18, and between the exterior of the shank 18and the walls of the pocket 15 in the sheath terminal portion.

For this method of application, the material 22 must necessarily be in aplastic or flowable condition when it is first placed in the pocket orchamber 15, and the material 22 is preferably such that it is or becomesand remains elastic and of a nature to adhere to the various surfaceswith which it is in contact, and particularly to the exterior of theterminal pin 12, the walls of the pocket 15, and the interior andexterior of the shank 13. The material 22 is also preferably such thatit expands during the curing or polymerization under the influence ofheat, and since it is closely confined in the pocket 15 within apredetermined area, will be tightly pressed against all surfacesdefining the area.

As one example of a satisfactory material to form that part of theclosure indicated at 22, a suitable uncured or slow curing siliconerubber, preferably having admixed therewith up to twice its weight ormore of a substance suitable as a filler, may be used. The preferredproportions of the admixture depend on such factors as the specificingredients and the specific application, one example beingapproximately equal parts of the silicone rubber known commercially asSilastic 120 and zircon ground to as fine as minus 400 mesh or finer.

The cover or bushing 16 is held tightly in position in overlyingrelation with the open end of the sheath 13 in order to closely confinethe material 22 within a predetermined area in the open end of thesheath whereby expansion of the material 22 on curing or polymerizationwill press the material tightly against the surfaces and provide a tightand effective seal. As illustrated in Figures 1 and 2 of the drawings,an electrical conductor wire 24 is secured to the terminal pin 12 bymeans of a deformable ring 25 which surrounds the conductor wire 24 andthe terminal pin 12 and is crimped as at 26 to secure the conductor wire24 tightly to the terminal pin 12. The crimped connection between theconductor wire and the terminal pin is so positioned with respect to thecover or bushing that either the deformable ring 25 or the end 27 of theconductor wire 24 is pressed tightly against the cover or bushing 16 tohold the cover or bushing in position with respect to the open end ofthe sheath. As is usual, the conductor wire 24 is provided throughoutits major length with insulating covering 23 which is in this instancepreferably of rubber, or rubber-like material, or at least a materialwhich is sufiiciently compatible with a moldable vulcanizable outercover to provide a tight sealing joint.

The closure for the open end of the sheath 13, as illustrated herein,comprises, as a third element, a moldable material 29 which is capableof being molded about the end of the sheath 13 adjacent the open endthereof, the terminal pin 12 extending beyond the cover or bushing 16,and about at least a portion of the length of. the insulating material.surrounding the conductor wire 24. The material 29 is preferably suchthat it may be shaped by a mold such as illustrated at 3!) in Figure 4and cured or polymerized into a flexible elastic covering by beingsubjected to heat, and also such that the material will vulcanize intotight sealing engagement with the exterior surface of the end of thesheath 13 and with the insulating covering 28 on the conductor wire 24.The material is also such that after being placed in the mold andsubjected to heat it will flow in a manner to closely engage all of theparts heretofore mentioned. The heat supplied to the material 29 tocause the same to flow and vulcanize will simultaneously be effective tocure or polymerize the material 22.

In order to insure sealingly tight adherence of the material 29 to theend of the sheath 13 adjacent the opening therein there is provided asleeve or ferrule 31 which may be of any material compatible with thematerial 29 insofar as the material adhering thereto and forming a tightseal therewith, surrounding the exterior of the sheath 13 adjacent theopening therein and closely secured in tight sealing engagement with theexterior of the sheath to prevent leakage between the innercircumference of the sleeve or ferrule and the outer circumference ofthe sheath 13 as, for example, where the sleeve or ferrule is of brass,by means of solder 32. Such sleeve or ferrule 31 is also preferablyprovided with an annular outwardly extending flange or shoulder at theend thereof furthest removed from the opening in the sheath 13. As shownin Figure 4, such flange or shoulder 33 may be such that it willcooperate with one end of the mold cavity 34 through which the sheath 13extends to prevent extrusion of the moldable vulcanizable material outof the mold and along the length of the sheath 13. It will be understoodthat the amount of moldable vulcanizable material initially placed inthe mold recess must be suflicient so that when the material issubjected to heat such material will be caused to flow about all partswhich it is to cover and will compietely surround such parts as shown inFigure 2. It is understood, however, that various types and shapes ofmolds may be utilized, as well as various methods of applying themoldable vulcanizable cover to the various parts of the electric heater,and the sleeve or ferrule may be made of various materials as long assuch material is compatible in forming a tightly adherent bond with thematerial 29.

In Figure 5 there is shown a modified form of the invention wherein inplace of the shouldered sleeve or ferrule 31 there is provided anannular U-shaped ring 35 having a hub 36 provided with a central openingfor receiving the heater sheath 13, and also having an outer wall 37,thus forming a cup-shaped cavity facing toward the terminal end of thesheath 13. Assuming the ring 35 to be of a metal, for example, brass,which is compatible with the moldable material 29 insofar as forming atightly adhering seal therewith, the ring 35 is positioned on the sheath13 adjacent to terminal opening and secured thereto by soldering orotherwise as indicated at 38 to provide a sealingly tight relationbetween the hub 36 and the sleeve 13 that will prevent leakage ofmoisture therebetween. Otherwise, the method and steps of the assemblyof the parts is the same as hereinbefore described, with the moldablematerial 29 forming a sealingly tight joint with the surfaces of thering 35 with which it is in contact and forming a continuous coveringfrom the ring 35 to and including the leading end of the insulation 28on the electrical conductor 24. The mold 30 may be such as toaccommodate this construction.

Referring to Figure 6, the invention herein disclosed is shown as beingapplied to a sheathed embedded-resistor heater in which the sheath isbent in, for example a U- shape with the two ends of the sheath lyingadjacent each other and in substantially parallel relation. As shown inthis figure, the ring 39 is provided with two spaced hubs 36, eachprovided with a central opening through which the respective ends of thesheath 13 extend. With this construction, the insulated portions 28 ofthe electrical conductors 24 may lie side by side, and the material 29is molded about the entire assembly to provide a continuous coveringfrom the ring 39 to at least the leading ends of the insulation on'therespective electrical conductors 24. The material 29 also flows betweenthe respective ends of the sheath 13 and associated parts to provideinsulation between the respective ends of sheath 13 as well as a fluidtight covering.

In Figure 8 of the drawings it is illustrated that the constructiondescribed in Figures 1 and 2 is adaptable to use with an arrangement ofheater sheath wherein the heater sheath is bent, for example, in U-shapeand wherein the adjacent ends of the sheath lie relatively closely toeach other and in substantially parallel relation. As shown in thisfigure, the material 29 is molded about the sleeves or ferrules 33 onthe respective ends of the sheath 13 in a manner to provide a singlecomplete covering for the pair of sleeves or ferrules 33 on therespective adjacent ends of the sheath 13.

What is claimed is:

l. A sealing closure for the terminal end of an electric heating devicehaving a resistor means including a terminal and sheath means generallyenclosing said resistor means, and provided with a tubular portiondefining an opening through which said terminal extends, said closurecomprising a moldable material surrounding and forming a sealed jointwith the exterior of the tubular portion of the sheath adjacent theopening therein and with the resistor terminal extending outwardly ofsaid opening, a sleeve surrounding the tubular portion of the sheathmeans defining said opening and of a material compatible with saidmoldable material to the extent of forming a tight sealing jointtherewith, and a radially extending flange on said sleeve adjacent theend thereof removed from the opening in said tubular portion and againstwhich said moldable material abuts.

2. A sealing closure for the terminal end of an electric heating devicehaving a resistor means including a terminal and sheath means generallyenclosing said resistor means, and provided with a tubular portiondefining an opening through which said terminal extends, said closurecomprising a moldable rubber-like material surrounding and forming asealed joint with the exterior of the tubular portion of the sheathadjacent the opening therein and with the resistor terminal extendingoutwardly of said opening, a sleeve surrounding the tubular portion ofthe sheath means defining said opening and of a material compatible withsaid moldable material to the extent of forming a tight sealing jointtherewith, and a radially extending flange on said sleeve adjacent theend thereof removed from the opening in said tubular portion and againstwhich said moldable material abuts.

3. In combination with a sheathed resistor-type electric heater having aresistor terminal electrically connected to an insulated conductor wireand a fluid-tight seal extending from the insulation of said conductorwire to the sheath of said heater, said seal enclosing the electricalconnection between the resistor terminal and said conductor wire andprotecting said connection from contact with foreign matters, a coveringsurrounding the sheath, said covering being of a material compatiblewith said sealing material to the extent of forming a fluid-tight jointtherewith, and a radially extending flange on said covering and againstwhich the sealing material abuts.

4. A closure for the resistor terminal opening of a sheathed-embeddedresistor electric heater, comprising a sealing material disposed in theterminal opening and surrounding the resistor terminal, an exteriorcovering for the sheath and the resistor terminal including a moldablematerial surrounding and forming a sealed joint with the sheath and theresistor terminal, and a sleeve surrounding the sheath, said sleevebeing of a material compatible with said sealing material to the extentof forming a fluidtight joint therewith, and a radially extending flangeon said sleeve and against which the sealing material abuts.

5. A sealing closure for the terminal end of an electric heating devicehaving resistor means including a terminal and also having sheath meansgenerally enclosing said resistor means and provided with a tubularportion defining an opening through which said terminal extends, saidclosure comprising moldable rubber-like material and a sleeve ofmaterial sealingly compatible with said moldable material, said sleeveengaging and surrounding said tubular portion and said moldable materialengaging and surrounding and forming a sealed joint with said sleeve andwith the terminal extending outwardly of said opening.

6. A sealing closure for the terminal end of an electric heating devicehaving resistor means including a terminal and sheath means generallyenclosing said resistor means and provided with a tubular portiondefining an opening through which said terminal extends, said closurecomprising a sleeve surrounding said tubular portion and fixed theretoin fluid-tight relation, and a moldable material engaging andsurrounding said sleeve, said sleeve being formed of material which iscompatible with said moldable material to the extent of forming a tightsealing joint therewith.

7. In combination with a sheathed resistor-type electric heater having aresistor terminal electrically connected to an insulated conductor wire,comprising rubber-like moldable material, and a sleeve of materialcompatible with said moldable material and securely engaging andsurrounding the terminal end of said heater, said moldable materialbeing molded to enclose the electrical connection between the resistorterminal and the conductor wire and extending from sealing engagementwith the insulation of said conductor wire to sealing engagement withsaid sleeve to protect said electrical connection from contact withforeign matter and to seal the terminal end of said heater againstentrance of foreign matter.

8. In an electric heating device including resistor means having aterminal, sheath means enclosing said resistor means and provided withanopening through which said terminal extends, and a conductor wire havingelectrical connection with the extending portion of said terminal andhaving an insulating covering, the method of forming a seal at theterminal end of said heating device which comprises, surrounding theexterior of the sheath adjacent said opening with a sleeve formed ofmaterial which is compatible with a heat moldable material to the extentof forming a fluid-tight joint therewith, securing said sleeve to saidsheath in fluid-tight relationship and molding a heat moldable materialabout said sleeve and said electrical connection and the insulation ofsaid conductor with application of sufiicient heat to form a sealedjoint between said heat moldable material and the surfaces with which itis in contact.

9. A sealing closure for the terminal end of an electric heating devicehaving resistor means including a terminal and also having ferroussheath means generally enclosing said resistor means and provided with atubular portion defining an opening through which said terminal extends,said closure comprising a sleeve of non-ferrous material engaging andsurrounding said tubular portion and a moldable material engaging andsurrounding said sleeve covering, the latter being formed of materialwhich is compatible with said moldable material to the extent of forminga tight sealing joint therewith.

10. A sealing closure for the terminal end of an electric heating devicehaving resistor means including a terminal and ferrous sheath meansgenerally enclosing said resistor means and provided with a tubularportion defining an opening through which said terminal extends, saidclosure comprising a brass sleeve surrounding said tubular portion andfixed thereto in fluid-tight relation, and a rubberlike material moldedabout said tubular portion and in compatible sealing relation with saidsleeve.

11. A sealing closure for the open end of an electric heating devicehaving a resistor conductor encased in a tubular protective sheath, thecombination comprising a terminal conductor electrically connected tosaid resistor and extending outwardly of an open end of said sheath, aninsulated conductor wire having an electrical connection with theextending portion of said terminal conductor, insulating materialenclosing said electrical connection, said insulating material beingcontiguous to the open end of said sheath and extending therefrom andinto sealing engagement with the insulation of said conductor wire, andmetallic means in sealing contact with a peripheral surface adjacent tothe open end of said sheath and with the contiguous insulating materialand interposed therebetween to insure compatible scaling relationthereof.

References Cited in the tile of this patent UNITED STATES PATENTS2,489,998 Charbonneau et al Nov. 29, 1949 FOREIGN PATENTS 557,765 GreatBritain Dec. 3, 1943

